Method of increasing recovery from oil reservoirs



Augylylg H. L. sToNEj METHOD of INCREASING. RECOVERY mou on. volss Filed Dec, V18. 1957,.' 2 Shaets-he'e't I '-sEPAnAToR Aolwmisson I7 Y I A A s3 A NoN--Umcu 'fogigmA'L huisjes uoulo Lum {MNED nuwmvnuso 55m/0'* .0 zong:

'zone 3 I 1 Y F56.; 2A. l INVNTOK HERBERT L. STONE ATTORNEY.

iin-ritje States arent @thee assiste Patented Aug. i 1961 mmol) or INCREASING itncovEn-r FROM ou.

i v nasnnvoins f l Herbert L.v Stone, Houston, Tex., assgnor, by meme assigniments;l 'to 'Iuls.a,.-Okla.,a corporation of'Delaware FiledDec. 18, 1957, Ser. No. 703,681-

zclaims. (ci. 16e-7) 'Jersey Production Research Company,

` contained-in the reservoirs.

Current oil productionI practices fail to recover much of the 011 originally in place in natural reservoirs. As a consequence thereofy much effort has been devoted 'injection well 12 and oil is to devising methods of improving the'ultimate recovery f of the-oil in the reservoirs. One such method for im- .proving'recovery of oil consists in displacing the reservoir oil withva hydrocarbon mixture as, for example. a

hydrocarbon fluid'usually containing methane and higher molecular weight hydrocarbon components. The solution of these components in the residual oil, especially the components less volatile than methane. leads to high oil recovery. An' oil whichvhas been diluted byextensive solution of these components (that is, lighter hydrocarbons such as'ethane, propane. butano, pentane', etc.) or g. -a natural gas which contains large quantities of these com- .ponente is said to be enriched Thismethod, however, requires the injection of large v volume of the hydrocarbon-mixture, which volume is diicult and expensivejto obtain.

Most natural reservoir oils have dissolved in them large i quantities of'llight hydrocarbons, such as methane, ethane,

- 2?. liesbetween production well'13 and zone 21 and inpropane, butane, pentanejetc. vWhen ,these lighter hy-"v Y drocarbons are separated from heavier hydrocarbon com- 'Y ponents in a separator or distillation column` the result- 4ing more volatile mixture is of a composition sufficiently enriched with intermediate hydrocarbons (cthane, propane, butane, etc.) as to give highoil recoveries. However, when oil Ais-produced from areservoir and separated into a light component 'phase and a heavy component phase and the light component phase compressed and reinjected intothe formation, the reservoir pressure declinesvbe'causeof the removal of the heavy component phase.v A pressure decline in the reservoir interferes with` ultimate recovery of the oil.

Briey, this invention comprises the steps of producing from a subsurface reservoir through a production well, separating the produced oil into a fluid phase containing .light hydrocarbon components and a liquidphase containing heavier hydrocarbon components;` injecting the light hydrocarbon components into the reservoir through a first injection well, the first injection well being spaced from' the production vwell and then injecting the heavier .hydrocarbon components into the reservoir through a second injection well, said second injection well being spaced from the production well andthe rst injection Weil.

2 i, FIG. 2. is a schematic view, illustrating another embodimcnt of the invention. .f

Referring to FIGS. l and 2 more specifically, numeral .1() designates the surface of the earth upon which are arranged injection wells 11 and 12, a production well 13, aseparator 1S, a pump and a compressor 17. yAn oil reservoir 14 is located below the surface of the earth 10 as shown. Injection wells 11 and 12 and production well 13 extend below the surface of the earth 10 to reservoir 14. On the surface of the earth production Well 13 uidly connects with separator 15, which is, in turn,

connected to pump 16 and compressor 17.

As illustrated in the drawings a light hydrocarbonv mix--V ture is being injected through injection well 11, a heavy hydrocarbon liquid mixture is being injected through A13. Zones 22 and 24 may or may not exist depending upon the length of time the operation has been conducted.

Tnc embodiment illustrated in FIG. 2 is similar-except production well 13 isv positioned between injection wells -11 and i2. Thus for the operation described supra an enriched fluid invaded zone 20 is formed adjacent injection well 1 1 and non-enriched fluid invaded zone 21 is adjacentzone 2i). However, original reservoir oil zone jected liquid zone 23 extendsfrominjection well 12 to ln both embodiments reservoir oil is produced from production well 13 and sent to separator 15 where the oil is separated into. a fluid .containing the lighter hyarrowed line 25 wherein the uidphase is compressed to a pressure sulcient to displace the reservoir oil. From compressor 17 the tluidis sent to injection well 11 as indicated 'by arrowcd line 26. The stripped liquid from the .-separator is sent to pump 16, as indicated by arrowed line An object of the invention, therefore, is to provide a method for improving recovery of reservoir oil by preventing or lessening reservoir pressure decline when displacing 'reservoir oil with a light hydrocarbon mixture separated from produced reservoir oil wherein the pressure decline inhibitor is easy and economical to obtain and consists of a recycled heavier hydrocarbon phase.

This and other objects of the invention will be appar- FIGA is aschematic view illustrating one embodiment i fof the method'of the invention; and

'27, wherein the liquid phase is pumped to a pressure suicient to displace the 'reservoir oil.v From pumpvl the liquid is sent to injection well 12, as indicated by arrowed 1 The practical size of the enriched uid bank (zone 2.0)y is limited by 'two' factors. (l) After the linjected liquid zone 23 reaches the production well 135 the produced lluid will yield much less light hydrocarbons than before. Continuing the operation involves recycling-large qauntities ot' oil which previously have been produced and stripped of lighter components. Therefore, to `determine the optimum location of injection well 12, it is Y j assumed that the return of stripped liquid to the reservoir will be stopped when stripped liquid begins to be produced from well 13. (2) When the enriching components of zone 20 reach injection well 12, the uid injected through well 11 then will be dissolving in the liquid injected'through well 12 and zone 20 will have ceased'v growing. Thus, the optimum location of liquid injection well 12 is such that zone 2,0 reaches injection well 12 at the same time that zone 23 reaches production well 13.

being produced through pro-- with the v 'embodi- ,This location may be determined approximately as follows:

i Laboratory displacement experiments are conducted 'wherein a model linear reservoir of length L' is completely charged with oil and connate water at actual res- A ervoir temperature and pressure to simulate actual reservoir conditions. The lmodel-porous medium has permeability and porosity characteristics similar `to-the actual reservoir characteristics. A fluid hydrocarbonk mixture ofthe same composition to be injected through inthe .experimental reservoir to, the length of the experimental reservoir is evaluated at the time the injected enriched iiuidis first produced. v

. For purposes of calculation.v a linear system is'considered where L1 is the distance between injectionwell 11 "-1 and injection well 12; I1 is the length of zone l20at any time; L2 is the distance between injection 1 well- 12 and production well 13; Zz'is theflength of zone 23 at any timejL is the total length of the reservoir; fp is the porosity of the reservoir;.G is the cumulative-volume (at reservoir conditions) of liuid injected intowell 11 per unitof cross-sectional area of the reservoiraO is 'the volume of oil-`(at reservoir conditions) injected, through injection ivell 12 per unit o'cross-sectional area ofthe reservoir. I 'Ihen, at yany given time Y j As Zone. fill-reaches injection'well 12 at the'sametime that zone Z4 reaches production well i3,

Similar relationships to determine the optimum locationof injection lwell 12 can be derived for non-linear -reservoirs.. Thevalue L1 represents the minimum desirable value in all cases.` In some instances, it may be desirable to relax the first restriction, that is to allow simultaneous production of injected'oil and reservoir oil. Such larger than indicated by Equation l. However, this increase will. be limited by the practical problems of handling the resulting large volumes of produced fluids.

` in the embodiment of FIG. 2 the'lrelative locations of production well 13 and injection well 12 are reversed.

APlflxus, production is from the center of the-reservoir and time as the stripped injection lluid (zone 2l) reaches production well 13. An additional factor F is employed 70 injection well at approximately the same time said heavy which is similar to E, i.e., it is the ratio of the total 'volume of fluid injected per unit cross-sectional area of theex'perimental reservoir to the length of the experimental reservoir. However (F) is evaluated at the time of stripped gas (gas in equilibrium with the reservoir oil) breakthrough rather than at the time injected ene v 'r The ratio E of thetotal 4 richedlluid is first-produced. Also thelength of zone 2li is designated I3.. l

The location of the-central production well i3 andthe length or" the enriched zone l1 are determinedas follows:

- The ratio G/O in Equations l and 2 is equal to'the gas-oil ratiotat reservoir conditions)l of the fluid pro- 'duced from well 13.

Y The choice of the arrangement for the injection wells and the production well is determined by which gives the greater length-of enriched zone L1.

At any'desired time the recycling operation may be halted and extraneous gas injection at injection well 11. This gas may be rich in intermediates or it may be a lean gas consisting principallyA of 'methane or 40 even of more insoluble materials such as air or nitrogen.

Whatever typegas is injected, recovery of oil will be enhanced by the presence of the enriched zone 20.

For purposes of illustration the description herein reters yto single tlu'id injection, liquid injection and production wells.- -However, it is to be understood the invention encompasses the more 'practical arrangement wherein a V`v`plurali-ty of nid injection, liquid injection and production wells are used. v

Having fully4 described the nature, objects, and opere ation of my invention, I claim:

l. A method for increasing recovery of oil from a a uid phase containing. substantially light hydrocarbon recycling or the oil will permit L1 to be made somewhat vcon-iponents having no more :than 6A carbon atoms per molecule and a liquid phase containing substantially heavy hydrocarbon components having more than 6 carbon atoms per molecule; and simultaneously while producing oil from said reservoir, injecting said light hydrocarbon components into Said reservoir through at least one lrst injection well to displace reservoir oil to said production well and said heavy hydrocarbon components into said reservoir through at least one second injection well to inhibit reservoir pressure decline, said second injection well being Ilocated between said first injection Welland said production well, and selectively spaced therefrom in a manner such that said light hydrocarbon components injected through said first injection well-reach said second hydrocarbon components injected through said second injection well reach said -production well.

'2. A method for increasing recovery of oil fro'ma subsurface reservoir comprising the steps of producing oil from said reservoir through at least one production well;

segnata-ting said produced oi-l into only two phases, a uiid phase containing.substantially light vhydrocarbon compohent's .having-*no more than 6 carbon atoms per mole- "culeiand a liquidphase containing substantially heavy well andv said heavy hydrocarboncomponents-into said roilfrorn said reservoir, injecting'said light-hydrocarbon components i-n-to said reservoir through at least one. first injection `well to displace reservoir oil to said production first injection well reach said productionfwell atfapproxiv mately the same time said heavy hydrocarbon components injected through said second injection well reach said production well.

References Cited in the ille of this patent UNITED STATES PATENTS Garrison Sept. 26, 1944 2,412,765 Buddrus Dec. 17, 1946 2,867,277 Weinaug et al. Jan. 6, 1959 1,927,637- Draper e Mar. 8.l 1960 I FOREIGN PATENTS 726,712

f Great Britain t Mar. 23,1955 

